View Full Version : Gear Ratio Question

08-05-2008, 11:08 AM
OK here is my set up.

I just did a EJ20K swap with the tranny swapped also into a 99 legacy gt auto.

Do I need to change my rear diff and if I do what gear ratio do I need to look for?

Will a rear diff out a '03 5speed WRX work?

Thanks for the help.


08-05-2008, 11:11 AM
You need to make sure the FD of your tranny matches the rear diff.

08-05-2008, 01:29 PM
post up your tranny code and the tranny code off the tranny you're swapping in, i can tell ya what the final drives are.

Your code can be found under the hood *Silver plate*

08-05-2008, 02:14 PM
A factory rear diff from an 02-05 5mt wrx will only work with an 02-05 wrx tranny. The rear diff has a 3.545 ratio and the front has a 3.900.

This works out because of the 1:1.100 center differential in the 5mt wrx tranny.

Find out your FD ratio. It should be 4.444, but I could be mistaken. If not 4.44, it's 4.11, and either way you will have a large range of diffs to choose from.

08-05-2008, 02:44 PM
Hey I got the TY #


Now I've been told that the EJ20K manual is 4.44... well I just need what will work.

Thanks for quick replys!!!


08-05-2008, 04:23 PM
Yes, the ej20k tranny does in fact have a 4.444 gear ratio. Therefore you will need a 4.444 rear diff and the 03 5mt wrx diff you found will not work.

What is the tranny # from your stock tranny? The one you gave is from the ej20k tranny.

08-06-2008, 09:33 AM
I'll get that later tonight.

Now what about the foresters? I heard that they might have a 4.444 rear diff? can anyone confirm that?

08-06-2008, 08:32 PM
Yes, 04+ Forester XT's and Baja Turbos had 4.444 rear LSD's.

If you're just looking for an open diff, go check the classifieds, there's a guy selling his 4.444 from his 98 outback.

08-07-2008, 02:33 PM
Now correct me if I'm wrong if his auto 98 Legacy Outback has a 4.444 rear why would my auto 99 legacy gt not?

I'll have the TY# from the stock tranny by the end of the day.

08-07-2008, 04:28 PM
Now correct me if I'm wrong if his auto 98 Legacy Outback has a 4.444 rear why would my auto 99 legacy gt not?

They used shorter final drive ratios on the Outback because it has taller tires.